Conventionally, reduction in startup time and energy efficiency are desirable features for an image forming apparatus such as a printer, a copier, or the like. Therefore considerable attention has been attracted by a fixing unit that uses a heating rotary belt enabling a reduction in the heat capacity.
Furthermore, considerable attention has been directed to a fixing unit that uses an induction heating method (IH) for generating heat in a heat generating layer of the heating rotary belt by an electromagnetic induction action due to magnetic flux generated by an induction coil.
A fixing unit using a heating rotary belt includes a heating rotary belt, a pressing member, and a pressure rotor. The pressing member is disposed in an inner portion of the heating rotary belt, and abuts with an inner surface of the heating rotary belt. The pressure rotor sandwiches the heating rotary belt with the pressing member and is opposed to the heating rotary belt. The heating rotary belt may deform into an ellipse shape upon application of a pressing force from the pressure rotor to thereby expand in a direction orthogonal to the direction of pressure from the pressure rotor. The heating rotary belt may deform by a deformation amount as a result of the fluctuation in the intensity of the pressing force from the pressure rotor.
As described above, deformation of the heating rotary belt may be caused in a fixing unit that includes a combination of an induction heating method (IH) and a heating rotary belt. Consequently, heating efficiency in the fixing unit may vary in response to a fluctuation in the distance between the induction coil and the outer peripheral surface of the heating rotary belt. As a result, it has sometimes not been possible to stabilize the temperature increase time when starting up the fixing unit.
However, there is a fixing unit that stabilizes a heating efficiency by enabling an adjustment of the distance between the induction coil and the outer peripheral surface of the heating rotary belt by displacement of a support member that supports the induction coil.
A configuration to enable displacement of the supporting member in a fixing unit as described above is complicated. Furthermore, this type of fixing unit does not enable a reduction in the deformation of the heating rotary belt.